This invention relates generally to electrophotographic printing machines, and more particularly the invention is directed to a heated fuser roller and a pressure roller fusing assembly, in such a machine, including an ink contamination-free Release Agent Management (RAM) system having a low energy surface metering roller for effectively applying release agent to the heated fuser roller, thereby preventing toner image defects from release agent starvation for example.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roller or to a latent image on the photoconductive member. The toner attracted to a donor roller is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed rollers at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rollers with the toner image contacting the heated fuser roller to thereby effect heating of the toner images within the nip.
In order to prevent the toner images from offsetting back onto the heated fuser roller, such a fusing system or assembly usually includes a release agent management (RAM) system for applying a release agent or oil onto the surface of the heated fuser roller.
It has been found that contamination of such a RAM system occurs as early as 3K prints or images have been fused when such prints or images are preprinted forms having preprinted areas and toner filled areas being fused. This problem is common with preprinted forms because hundreds of different inks are used in producing the preprinted areas, and often without dryers in the ink compositions. One reason is because such dryers are costly, and thus they are not used as often as is necessary. Additionally, some inks require over 72 hours to completely dry, thus preprinted forms may reach a toner fill-in and fuse operation before they are completely dry. Consequently, during fusing of the toner filled-in areas of such preprinted forms, ink that is not completely dry transfers from the preprinted form to the heated fuser roller, to a donor roller of the RAM system, and then to a conventional metering roller of the RAM system. Agravated by the inks not being completely dry, the adhesive forces of the ink to the rollers are believed to be higher than cohesive forces that should be holding the inks together.
Following is a discussion of some prior art, incorporated herein by reference, which may have some relevance to the question of patentability, and which, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 4,214,549 granted to Rabin Moser on Jul. 29, 1980 discloses a heat and pressure roller fusing assembly for fixing toner images to copy substrates, the toner comprising a thermoplastic resin. The assembly includes an internally heated, fuser roller cooperating with a backup or pressure roller to form a nip through which the copy substrates pass with the images contacting the heated roller. The heated fuser roller is characterized by an outer surface or surface which by way of example is fabricated from a silicon rubber or Vitont.TM. material to which a low viscosity polymeric release fluid is applied. Release fluid is contained in a sump from which it is dispensed by means of a metering roller and a donor roller, the former of which contacts the release fluid in the sump and the latter of which contacts the surface of the heated fuser roller.
U.S. Pat. No. 5,500,722 granted to Robert M. Jacobs on Mar. 19, 1996 relates to a Release Agent Management (RAM) system for a heat and pressure fusing assembly for fixing black toner images in low and high volume imaging machines and also for fixing color images. An auxiliary oil supply is provided for applying extra oil to an oil impregnated web. The extra oil improves fuser roller release life in every application. Also, enables color fusing which requires higher oil application rates.